1. Technical Field
The invention relates to formulations and processes for random copolymers. More particularly, the invention relates to formulations and processes for preparing random copolymers having properties that may be particularly desirable for preparing thermoformed and blow molded articles.
2. Background of the Art
Propylene materials are among the most versatile and commonly used thermoplastics in the world today. Commercial grade polypropylenes are typically produced using either a Ziegler-Natta, succinate or metallocene catalyst mechanism in a polymerization process. Many industries, such as the packaging industry, utilize these polypropylene materials in various manufacturing processes, such as extrusion, injection molding, thermoforming and blow molding to create a variety of finished goods.
Within the packaging industry, there may be a number of unique applications that ideally require strong and substantially clear polymers. Medical articles, food storage containers, and other products that may readily be formed by thermoforming and blow molding techniques are used in various applications where they are in direct contact with blood or other bodily fluids, or with food or other items that are to be ingested or taken into the body. For these uses it may be desirable to use polymers having high clarity and strength and a very low extractables content.
Thermoforming and blow molding are two of the most rapidly growing technologies in rigid plastics processing. These manufacturing methods require certain desirable properties and characteristics of polymers to achieve better processability. Traditionally, Ziegler-Natta catalyzed polypropylenes have been used in these applications because they may exhibit greater strength and stiffness in the finished product. However, it is generally known that other types of polypropylenes, such as the metallocene catalyzed polypropylenes, may exhibit lower extractables and higher clarity. Despite these advantages; however, thermoforming and blow molding of metallocene catalyzed polypropylenes have been generally avoided, because the metallocene polypropylenes also usually have a narrower molecular weight distribution and somewhat lower melt temperature than other available polymeric materials. These qualities are undesirable because they result in poor sag resistance.
Accordingly, it may be desirable in the art to discover a way to obtain, in a polypropylene, the advantages of relatively low extractables and relatively high clarity while avoiding or reducing the problems that are usually seen when metallocene catalyzed polypropylenes are employed in thermoformed and blow molded applications.